6o Bevel Pinions. ii In Fig. 72/5 we have the core box required for the arms of a machine-moulded spur wheel; its description will serve also for bevel wheels. A represents the casting to be obtained, having six arms, and the box at B is so designed as to core out a space of one-sixth of that within the wheel rim. The box being in the foundry is placed on a true table a, and after filling with loam, is smoothed off with straight-edged batten at b. Six of these cores being dried and blackwashed, a pattern for the boss of the wheel is now necessary to complete the mould. Small Bevel Pinions require the patience of the pattern maker. Referring to Fig. 73, which is the section of a bevel pinion, it will be seen that the teeth vary in size from A to B, and must, therefore, be entirely gouged out by hand. The body of the pattern is carefully turned as at c c, while blocks D, for the teeth, are planted on in hard wood and again turned, as in the last example. The section of the tooth now being set out by compass or template at A and B, the teeth have to be cut out and finished by hand. The teeth at B are made correctly lineable with those at A by means of the wooden spindle K, carrying a straight edge F so cut as to be always truly radial when moved round the surface A B.